People living near busy highways at increased risk of dementia, Canadian study finds

Health hazards of air and noise pollution are well known and joining the fray of such hazards is the increased risk of dementia, researchers in Canada have said.

According to a study published in The Lancet and led by researcher at Public Health Ontario and the Institute for Clinical Evaluative Sciences (ICES), people residing near busy highways are at an increased risk of developing dementia – up to 12 per cent increased risk than people not living near such areas. Dementia is a group of memory-loss disorders including Alzheimer’s disease.

The findings are based on results of the study wherein scientists tracked all the adults living in Ontario, Canada—about 6.6 million people—over the course of a decade from 2001 to 2012. Using postal codes and medical records, they determined how close a given resident lived to a major road—including freeways, highways, or congested roads with two or more lanes—and if they went on to develop dementia.

According to the findings of the study, residents living within 50 meters (55 yards) of a major road were between 7 to 12 per cent more likely to develop dementia, depending on the duration they had spent there. The fact that they lived in an urban or a rural area also affected the results. The risk dissipated until, 200 meters away from a major road, residents were at no more risk than those who lived further away, the report said.

Alarming numbers reveal that nearly half of adults in Ontario lived within 200 meters (219 yards) of a major roadway, and Dr. Ray Copes, chief of environmental and occupational health at PHO and an author on the paper estimates similar numbers for the United States.

As urban centres become more densely populated and more congested with vehicles on major roads, Dr. Copes suggests the findings of this paper could be used to help inform municipal land use decisions as well as building design to take into account air pollution factors and the impact on residents.

Key findings:

Using data held at ICES, the researchers examined records of more than 6.5 million Ontario residents, aged 20-85, and mapped them according to residential postal codes five years before the study started.

Between 2001 and 2012, 243,611 cases of dementia, 31,577 cases of Parkinson’s disease, and 9,247 cases of multiple sclerosis were identified in Ontario.

People who lived within 50 metres of high-traffic roads had a seven per cent higher likelihood of dementia than those who lived more 300 metres away from busy roads.

The increase in the risk of developing dementia went down to four per cent if people lived 50-100 metres from major traffic, and to two per cent if they lived within 101-200 metres. At over 200 metres, there was no elevated risk of dementia.

There was no correlation between major traffic proximity and Parkinson’s disease or multiple sclerosis.